Use of Specially Coated Powdered Coating Materials and Coating Methods Using Such Coating Materials

ABSTRACT

The present invention relates to the use of a particle-containing powdered coating material, wherein the surface of the particles is at least partially covered with a coating additive, in cold gas spraying, flame spraying, high-speed flame spraying, thermal plasma spraying and non-thermal plasma spraying. Furthermore, the present invention relates to coating methods, in particular the above-named methods, using the powdered coating material according to the invention.

The present invention relates to the use of specially equipped powderedcoating materials. Furthermore, the present invention comprises methodsfor substrate coating using specially equipped powdered coatingmaterials. Furthermore, the present invention comprises powdered coatingmaterials which are suitable for the above-named uses and/or methods.

A large number of coating methods for different substrates are alreadyknown. For example, metals or precursors thereof are deposited on asubstrate surface from the gas phase, see e.g. PVD or CVD methods.Furthermore, corresponding substances can be deposited for example froma solution by means of galvanic methods. In addition, it is possible toapply coatings for example in the form of varnishes to the surface.However, all the methods have specific advantages and disadvantages. Forexample, in the case of deposition in the form of varnishes, largeamounts of water and/or organic solvents are required, a drying time isneeded, the coating material to be applied must be compatible with thebase varnish, and a residue of the base varnish likewise remains on thesubstrate. For example, application by means of PVD methods requireslarge amounts of energy in order to bring non-volatile substances intothe gas phase.

In view of the above-named limitations, a large number of coatingmethods have been developed to provide the properties desired for therespective intended use. Known methods use, for example, kinetic energy,thermal energy or mixtures thereof to produce the coatings, wherein thethermal energy can originate for example from a conventional combustionflame or a plasma flame. The latter are further divided into thermal andnon-thermal plasmas, by which is meant that a gas has been partially orcompletely separated into free charge carriers such as ions orelectrons.

In the case of cold gas spraying, the coating is formed by applying apowder to a substrate surface, wherein the powder particles are greatlyaccelerated. For this, a heated process gas is accelerated to ultrasonicspeed by expansion in a de Laval nozzle and then the powder is injected.As a result of the high kinetic energy, the particles form a dense layerwhen they strike the substrate surface.

For example, WO 2010/003396 A1 discloses the use of cold gas spraying asa coating method for applying wear-protection coatings. Furthermore,disclosures of the cold gas spraying method are found for example in EP1 363 811 A1, EP 0 911 425 B1 and U.S. Pat. No. 7,740,905 B2.

Flame spraying belongs to the group of thermal coating methods. Here, apowdered coating material is introduced into the flame of a fuelgas/oxygen mixture. Here, temperatures of up to approximately 3200° C.can be reached for example with oxyacetylene flames. Details of themethod can be learned from publications such as e.g. EP 830 464 B1 andU.S. Pat. No. 5,207,382 A.

In the case of thermal plasma spraying, a powdered coating material isinjected into a thermal plasma. In the typically used thermal plasma,temperatures of up to approx. 20,000 K are reached, whereby the injectedpowder is melted and deposited on a substrate as coating.

The method of thermal plasma spraying and specific embodiments, as wellas method parameters are known to a person skilled in the art. By way ofexample, reference is made to WO 2004/016821, which describes the use ofthermal plasma spraying to apply an amorphous coating. Furthermore, EP 0344 781 for example discloses the use of flame spraying and thermalplasma spraying as coating methods using a tungsten carbide powdermixture. Specific devices for use in plasma spraying methods aredescribed multiple times in the literature, such as for example in EP 0342 428 A2, U.S. Pat. No. 7,678,428 B2, U.S. Pat. No. 7,928,338 B2 andEP 1 287 898 A2.

In the case of high-speed flame spraying, a fuel is combusted under highpressure, wherein fuel gases, liquid fuels and mixtures thereof can allbe used as fuel. A powdered coating material is injected into the highlyaccelerated flame. This method is known for being characterized byrelatively dense spray coatings.

High-speed flame spraying is also well known to a person skilled in theart and has already been described in numerous publications. Forexample, EP 0 825 272 A2 discloses a substrate coating with a copperalloy using high-speed flame spraying. Furthermore, WO 2010/037548 A1and EP 0 492 384 A1 for example disclose the method of high-speed flamespraying and devices to be used therein.

Non-thermal plasma spraying is carried out largely analogously tothermal plasma spraying and flame spraying. A powdered coating materialis injected into a non-thermal plasma and deposited with it onto asubstrate surface. As can be learned for example from EP 1 675 971 B1,this method is characterized by a particularly low thermal load of thecoated substrate. This method, particular embodiments and correspondingmethod parameters are also known to a person skilled in the art fromvarious publications. For example, EP 2 104 750 A2 describes the use ofthis method and a device for carrying it out. For example, DE 103 20 379A1 describes the production of an electrically heatable element usingthis method.

Further disclosures in respect of the method or devices for non-thermalplasma spraying are found for example in EP 1 675 971 B1, DE 10 2006 061435 A1, WO 03/064061 A1, WO 2005/031026 A1, DE 198 07 086 A1, DE 101 16502 A1, WO 01/32949 A1, EP 0 254 424 B1, EP 1 024 222 A2, DE 195 32 412A1, DE 199 55 880 A1 and DE 198 56 307 01.

However, a particular problem of coating methods using a powderedcoating material is that powdered coating materials form agglomerateswhich form a non-uniform coating when applied to the substrate surface.

An object of the present invention is to improve existing methods forsubstrate coating and to make possible novel methods for substratecoating. In particular the problems caused by agglomerates of thepowdered coating material are to be minimized or eliminated by thepresent invention.

Furthermore, the production of particularly thin layers is to be madepossible or simplified by the present invention.

Furthermore, the methods according to the invention are to make newcoatings available and/or make it possible to produce known coatings ofparticularly high quality.

A further object of the present invention is to provide a powderedcoating material which is particularly suitable for one of theabove-named uses in coating methods.

The present invention relates to the use of a particle-containingpowdered coating material, the surface of which is equipped with atleast one coating additive which has a boiling point or decompositiontemperature of below 500° C., in a coating method selected from thegroup consisting of cold gas spraying, flame spraying, high-speed flamespraying, thermal plasma spraying and non-thermal plasma spraying.

In particular embodiments of the above-named use, the weight proportionof the at least one coating additive is at least 0.01 wt.-%, relative tothe total weight of the coating material and the coating additive.

In particular embodiments of the above-named uses, the weight proportionof the at least one coating additive is at most 80 wt.-%, relative tothe total weight of the coating material and the coating additive.

In particular embodiments of the above-named uses, the particles of thepowdered coating material comprise or are metal particles, wherein themetal is selected from the group consisting of silver, gold, platinum,palladium, vanadium, chromium, manganese, cobalt, germanium, antimony,aluminum, zinc, tin, iron, copper, nickel, titanium, silicon, alloys andmixtures thereof.

In particular embodiments of the above-named uses, the carbon content ofthe powdered coating material is from 0.01 wt.-% to 15 wt.-%, in eachcase relative to the total weight of the coating material and thecoating additive.

In particular embodiments of the above-named uses, the compounds used ascoating additive have at least 6 carbon atoms.

In particular embodiments of the above-named uses, the coating method isselected from the group consisting of flame spraying and non-thermalplasma spraying. In particular ones of the above-named embodiments, thecoating method is preferably non-thermal plasma spraying.

In particular embodiments of the above-named uses, the at least onecoating additive is selected from the group consisting of polymers,monomers, silanes, waxes, oxidized waxes, carboxylic acids, phosphonicacids, derivatives of the above-named and mixtures thereof.

In particular embodiments of the above-named uses, the at least onecoating additive comprises no stearic acid and/or oleic acid andpreferably no saturated or unsaturated C18 carboxylic acids, morepreferably no saturated or unsaturated C14 to C18 carboxylic acids,still more preferably no saturated or unsaturated C12 to C18 carboxylicacids and most preferably no saturated or unsaturated C10 to C20carboxylic acids.

In particular embodiments of the above-named uses, the coating additivewas applied to the particles mechanically.

In particular embodiments of the above-named uses, the powdered coatingmaterial has a particle-size distribution with a D₅₀ value from a rangeof from 1.5 to 53 μm.

Furthermore, the present invention relates to methods for coating asubstrate selected from the group consisting of cold gas spraying, flamespraying, high-speed flame spraying, thermal plasma spraying andnon-thermal plasma spraying, in which a particle-containing powderedcoating material is used, wherein the particles are equipped with atleast one coating additive which has a boiling point or decompositiontemperature of below 500° C.

In particular embodiments of the above-named methods, the method isselected from the group consisting of flame spraying and non-thermalplasma spraying. The coating method is preferably non-thermal plasmaspraying.

In particular embodiments of the above-named methods, the powderedcoating material is conveyed as an aerosol.

In particular embodiments of the above-named methods, the mediumdirected onto the substrate is air or has been produced from air.

The term “powdered coating material” within the meaning of the presentinvention relates to a particle mixture which is applied to thesubstrate as coating. The equipping of the surface of the particles ofthe powdered coating material according to the invention need not beunbroken here. Without being understood as limiting the invention, theinventors are of the view that even a small application to or a smallcoverage of the surface of the particles of the powdered coatingmaterial is sufficient to break up agglomerates under the conditions ofthe coating method. In particular, the inventors are of the view that,because of the large gas volume of the coating additive appliedaccording to the invention to the particles or of its decompositionproducts, even small quantities of the coating additive are sufficientto break up any agglomerates present. The at least one coating additiveaccording to the invention is here applied to the surface of theparticles of the powdered coating material. In particular embodiments,it is preferred in particular that one (number: 1) coating additive isapplied. This provides the advantage that variations in the propertiesof the powdered coating material according to the invention as a resultof an incomplete mixing of the constituents of the coating additivebefore application to the particles are prevented. On the other hand, inother embodiments, it is preferred to use a mixture of at least twodifferent substances as coating additive. This can, for example, makepossible a simple adaptation of the properties of the powdered coatingmaterial according to the invention to different requirements. Thesubstances used according to the invention as coating additive can, forexample, be physically and/or chemically bound to the surface of theparticles. Furthermore, the coating additive can completely or partiallyenvelop the particles of the powdered coating material for example inthe form of coatings.

It has surprisingly been established that, by applying a coatingadditive with a low boiling point or decomposition temperature to thesurface of the particles of the powdered coating material during storageor following conveying, any agglomerates that have formed can be brokenup in the course of the coating method and particularly high-qualitycoatings are obtained. Furthermore, the use of the powdered coatingmaterial according to the invention allows a more uniform coating, withthe result that for example the production of particularly thin coatingsis made possible.

Methods according to the invention which can be used to build upcoatings are cold gas spraying, thermal plasma spraying, non-thermalplasma spraying, flame spraying and high-speed flame spraying. Asevaporation or decomposition of the coating additive is necessary,however, the variants of cold gas spraying according to the inventionare limited to embodiments in which a heated gas stream is used, withthe result that sufficient thermal energy for the evaporation ordecomposition of the coating additive is available. In particularembodiments of the present invention using cold gas spraying, it ispreferred in particular that the temperature of the gas stream is atleast 250° C., preferably at least 350° C., more preferably at least450° C. and still more preferably at least 500° C.

As the high speeds of the gas streams in cold gas spraying and inhigh-speed flame spraying give rise to only a short residence time ofthe powdered coating material in the gas stream or the flame, it can bedifficult in such methods to guarantee that the agglomerates break up ingood time. In particular embodiments, it is therefore preferred that themethod is selected from the group consisting of thermal plasma spraying,non-thermal plasma spraying and flame spraying.

As many coating materials are completely melted in the thermal plasma ofthe thermal plasma spraying and strike the surface of the substrate as aliquid, the additional outlay associated with the application of thecoating additive according to the invention to the surface of theparticles of the powdered coating material is uneconomical in particularcases, for example if no particularly uniform coating is to be achieved.In particular embodiments, the method is therefore selected from thegroup consisting of cold gas spraying, non-thermal plasma spraying,flame spraying and high-speed flame spraying, preferably from the groupconsisting of non-thermal plasma spraying and flame spraying.

The use of the plasma-based methods provides the advantage for examplethat even non-combustible gases can be used. This makes theindustrial-scale storage of the gases used easier, as for example therequirements in terms of safety technology are reduced. Where air isused, the gas required can optionally even be taken directly from theatmosphere. In particular quite particularly preferred embodiments, thecoating method is therefore selected from the group consisting ofthermal plasma spraying and non-thermal plasma spraying. In particularones of the above-named embodiments, it is preferred in particular thatthe method is non-thermal plasma spraying.

The coating additive applied according to the invention to the surfaceof the particles of the powdered coating material is characterized bythe above-named upper limit of the boiling point or decompositiontemperature. If the substance in question has both a boiling point and adecomposition temperature, only the lower temperature is considered. Itis not strictly necessary here that a gas is released when the coatingadditive decomposes. Without being understood as limiting the invention,any agglomerates present also appear to disintegrate duringdecomposition without releasing a gas. The inventors are of the viewthat, due to the decomposition of the coating additive, its surfaceproperties change and this change in turn leads to a disintegration ofthe agglomerates. In particular embodiments, however, it is preferred inparticular that, during decomposition, the coating additive usedreleases a gas which forces open any agglomerates present. The boilingpoint or decomposition temperature can be determined by means of methodsknown to a person skilled in the art. For example, the decompositiontemperature of polymers can be determined by means of thermogravimetryaccording to DIN EN ISO 11358.

The decomposition temperature or boiling point of the coating additiveto be applied according to the invention to the surface of the particleslies below 500° C., preferably below 470° C., more preferably below 440°C. and still more preferably below 420° C. In particular embodiments, itis preferred in particular that the decomposition temperature or boilingpoint of the substances applied to the surface of the particles liesbelow 400° C., preferably below 380° C., more preferably below 360° C.and still more preferably below 340° C.

The coating additives applied to the surface of the particles accordingto the invention need not be bound to the surface of the particles.However, in particular embodiments, it is preferred that the coatingadditives according to the invention are chemically and/or physicallybound to the surface of the particles. For example, in cases where thepowder must be able to be subjected even to larger mechanical loads, itcan be preferred that the coating additives are bound particularlysecurely to the surface of the particles. In particular embodiments,therefore, it is preferred that the coating additives are bound to thesurface with at least one type of chemical bond. Examples of chemicalbonds are covalent and ionic bonds. In further cases, where the coatingadditive must be able to be released again particularly easily, it canbe preferred in contrast that the coating additives are bound to thesurface of the particles only by means of physical bonds. In particularembodiments, therefore, it is preferred that the binding of the coatingadditives to the surface of the particles takes place only by means ofphysical bonds. Furthermore, it can be preferred that the coatingadditive forms a stable shell around the particles according to theinvention, with the result that for example no physical or chemicalbonds are necessary to hold the particles inside this shell. Withoutbeing understood as limiting the invention, the inventors are of theview that such a coating additive in the form of a stable shell withoutstrong bonds to the particles can be released particularly easily, asthe shell can already be released easily after a partial evaporation ordecomposition. In particular embodiments, therefore, it is preferredthat the coating additive forms a stable shell around the particles,wherein this shell does not have an opening that would be large enoughfor the particles to find their way out of the shell through it. Theterm “stable shell” within the meaning of the present inventiondescribes that the coating additive forms a shell around the particlesof the powdered coating material which is not destroyed under theconditions of storage and conveying.

The coating additives according to the invention can be applied to theparticles by means of a wide variety of methods. For example, coatingsof the particles can be obtained by polymerization of a monomer and/orfrom sol-gel processes. For example, stable shells consisting of thecoating additive can be obtained here. Furthermore, the coatingadditives according to the invention can be applied to the surface ofthe particles for example by deposition from a supersaturated solutionor by mechanical forces. Such methods are particularly suitable forapplying coating additives to large quantities of powdered coatingmaterial in a simple and cost-effective manner.

Without being understood as limiting the present invention, theinventors are of the view that the use of coating additives with a highcarbon content following the release of CO₂ makes possible aparticularly good breakup of the agglomerates. In particularembodiments, therefore, it is preferred that the weight proportion ofthe carbon atoms in the powdered coating material according to theinvention is at least 0.01 wt.-%, preferably at least 0.05 wt.-%, morepreferably at least 0.1 wt.-% and still more preferably at least 0.17wt.-%. In particular embodiments, it is preferred in particular that theweight proportion of the carbon atoms in the powdered coating materialaccording to the invention is at least 0.22 wt.-%, preferably at least0.28 wt.-%, more preferably at least 0.34 wt.-% and still morepreferably at least 0.4 wt.-%. The above-named wt.-% are based on thetotal weight of the coating material according to the invention and thecoating additive. The weight proportion of the carbon atoms to the totalweight of the powdered coating material according to the invention isdetermined for example with a CS 200 device from Leco Instruments GmbH.

On the other hand, in particular embodiments, it is preferred that theweight proportion of the carbon atoms in the powdered coating materialaccording to the invention is at most 15 wt.-%, preferably at most 10wt.-%, more preferably at most 7 wt.-% and still more preferably at most5 wt.-%. In particular ones of the above-named embodiments, it ispreferred in particular that the carbon content is at most 4 wt.-%,preferably at most 3 wt.-%, more preferably at most 2 wt.-% and stillmore preferably at most 1 wt.-%. The above-named wt.-% are based on thetotal weight of the coating material according to the invention and thecoating additive.

In particular embodiments, it is preferred in particular that the weightproportion of the carbon atoms in the powdered coating materialaccording to the invention is from a range of between 0.01 wt.-% and 15wt.-%, preferably from a range of between 0.05 wt.-% and 10 wt.-%, morepreferably from a range of between 0.1 wt.-% and 7 wt.-% and still morepreferably from a range of between 0.17 wt.-% and 5 wt.-%. In particularones of the above-named embodiments, it is preferred in particular thatthe weight proportion of the carbon atoms in the powdered coatingmaterial according to the invention is from a range of between 0.22wt.-% and 4 wt.-%, preferably from a range of between 0.28 wt.-% and 3wt.-%, more preferably from a range of between 0.34 wt.-% and 2 wt.-%and still more preferably from a range of between 0.4 wt.-% and 1 wt.-%.The above-named wt.-% are based on the total weight of the coatingmaterial according to the invention and the coating additive.

In particular embodiments, furthermore, it is preferred that thecompounds used as coating additive contain at least 6 carbon atoms,preferably at least 7 carbon atoms, more preferably at least 8 carbonatoms and still more preferably at least 9 carbon atoms. In particularones of the above-named embodiments, it is preferred in particular thatthe compounds used as coating additive contain at least 10 carbon atoms,preferably at least 11 carbon atoms, more preferably at least 12 carbonatoms and still more preferably at least 13 carbon atoms. The number ofcarbon atoms contained in the coating additive according to theinvention can be determined for example by determining the respectivecoating additive. All methods known to a person skilled in the art fordetermining a substance can be used here. For example, a coatingadditive can be removed from the particles of the powdered coatingmaterial using organic and/or aqueous solvents and then identified bymeans of HPLC, GCMS, NMR, CHN or combinations of the above-named witheach other or with other routinely used methods.

In particular embodiments, it is preferred to apply only a smallquantity of coating additive to the surface of the particles in order toprevent too strong a disruption of for example the plasma flame used forthe coating by the formation of large quantities of gas. In particularembodiments of the present invention, therefore, it is preferred thatthe quantity of coating additive is at most 80 wt.-%, preferably at most70 wt.-%, more preferably at most 65 wt.-% and still more preferably atmost 62 wt.-%. In particular ones of the above-named embodiments, it ispreferred in particular that the quantity of coating additive is at most59 wt.-%, preferably at most 57 wt.-%, more preferably at most 55 wt.-%and still more preferably at most 53 wt.-%. The above-named wt.-% arebased on the total weight of the coating material including the coatingadditive.

Furthermore, in particular embodiments using, for example, powderedcoating materials which have a particularly strong tendency to formsolid agglomerates, it can be advantageous to apply a minimum quantityof coating additive in order to ensure a breakup of the agglomerates. Inparticular embodiments, therefore, it is preferred that the quantity ofcoating additive is at least 0.02 wt.-%, preferably at least 0.08 wt.-%,more preferably at least 0.17 wt.-% and still more preferably at least0.30 wt.-%. In particular ones of the above-named embodiments, it ispreferred in particular that the quantity of coating additive is atleast 0.35 wt.-%, preferably at least 0.42 wt.-%, more preferably atleast 0.54 wt.-% and still more preferably at least 0.62 wt.-%. Theabove-named wt.-% are based on the total weight of the coating materialincluding the coating additive.

In further particular embodiments, it is furthermore preferred that theweight proportion of the coating additive is from a range of between0.02 wt.-% and 80 wt.-%, preferably from a range of between 0.08 wt.-%and 70 wt.-%, more preferably from a range of between 0.17 wt.-% and 65wt.-% and still more preferably from a range of between 0.30 wt.-% and62 wt.-%. In particular ones of the above-named embodiments, it ispreferred in particular that the weight proportion of the carbon atomsin the powdered coating material according to the invention is from arange of between 0.35 wt.-% and 59 wt.-%, preferably from a range ofbetween 0.42 wt.-% and 57 wt.-%, more preferably from a range of between0.54 wt.-% and 55 wt.-% and still more preferably from a range ofbetween 0.62 wt.-% and 53 wt.-%. The above-named wt.-% are based on thetotal weight of the coating material according to the inventionincluding the coating additive.

Examples of substances which can be used as coating additives within themeaning of the present invention are:

polymers (e.g. polysaccharides, plastics), monomers, silanes, waxes,oxidized waxes, carboxylic acids (e.g. fatty acids), phosphonic acids,derivatives of the above-named (in particular carboxylic acidderivatives and phosphoric acid derivatives) and mixtures thereof. Inparticular embodiments, it is preferred that polysaccharides, plastics,silanes, waxes, oxidized waxes, carboxylic acids (e.g. fatty acids)carboxylic acid derivatives, phosphonic acids, phosphoric acidderivatives or mixtures thereof, preferably polysaccharides, silanes,waxes, oxidized waxes, carboxylic acids (e.g. fatty acids) carboxylicacid derivatives, phosphonic acids, phosphoric acid derivatives ormixtures thereof, more preferably polysaccharides, silanes, waxes,oxidized waxes, carboxylic acids (e.g. fatty acids), carboxylic acidderivatives, phosphonic acids, phosphoric acid derivatives or mixturesthereof, and still more preferably polysaccharides, silanes, waxes,oxidized waxes, phosphonic acids, phosphoric acid derivatives ormixtures thereof, are used as coating additive.

The above-named waxes comprise both natural waxes and synthetic waxes.Examples of such waxes are paraffin waxes, petroleum waxes, montanwaxes, animal waxes (e.g. beeswax, shellac, wool wax), vegetable waxes(e.g. carnauba wax, candelilla wax, rice bran wax), fatty acid amidewaxes (such as e.g. erucamide), polyolefin waxes (such as e.g.polyethylene waxes, polypropylene waxes), grafted polyolefin waxes,Fischer-Tropsch waxes, and oxidized polyethylene waxes and modifiedpolyethylene and polypropylene waxes (e.g. metallocene waxes). The waxesaccording to the invention are bound only via physical bonds inparticular preferred embodiments. However, it is not ruled out that infurther particular embodiments the waxes have functional groups whichalternatively or additionally make a chemical bond, in particular anionic and/or covalent bond, possible.

The term “polymer” within the meaning of the present invention alsocomprises oligomers. In particular preferred embodiments, the polymersused according to the invention are, however, preferably built up of atleast 25 monomer units, more preferably of at least 35 monomer units,still more preferably of at least 45 monomer units and most preferablyof at least 50 monomer units. The polymers can be bound here to theparticles of the powdered coating material without covalent or ionicbonds being formed. In particular embodiments, however, it is preferredthat the coating additive according to the invention can form at leastone ionic or covalent bond with the particles of the powdered coatingmaterial. In particular ones of the above-named embodiments, such abinding preferably takes place via a phosphoric acid, carboxylic acid,silane or sulfonic acid group contained in the polymer.

The term “polysaccharide” within the meaning of the present inventionalso comprises oligosaccharides. In particular preferred embodiments,the polysaccharides used according to the invention are, however,preferably built up of at least 4 monomer units, more preferably of atleast 8 monomer units, still more preferably of at least 10 monomerunits and most preferably of at least 12 monomer units. In particularembodiments, particularly preferred polysaccharides are cellulose,cellulose derivatives such as e.g. methyl cellulose, ethyl cellulose,carboxymethyl cellulose, hydroxyethyl cellulose, hydroxypropylmethylcellulose, nitrocellulose (e.g. ethocel, or methocel from DowWolff Cellulosics), cellulose esters (e.g. cellulose acetate, celluloseacetobutyrate, and cellulose propionate), starches such as e.g. cornstarch, potato starch and wheat starch and modified starches.

The term “plastic” within the meaning of the present invention comprisesthermoplastic, thermosetting or elastomeric plastics. Because of thepossibility of adapting the properties of the plastics in a targetedmanner, it is preferred in particular embodiments that the additive is aplastic. For example, for the production of resistant, in particularhard, coatings of the particles according to the invention, the use ofelastomers and thermosetting plastics, in particular thermosettingplastics, can be preferred. In particular embodiments, the plastic usedaccording to the invention is therefore an elastomer or thermosettingplastic, preferably a thermosetting plastic. Furthermore, a particularlysimple application of the plastic for example by means of mechanicalforces can be to the fore and the use of thermoplastics can bepreferred. In particular embodiments, the plastic used according to theinvention is therefore a thermoplastic. Corresponding plastics which arecharacterized by a corresponding decomposition temperature or boilingpoint are known to a person skilled in the art and are found for examplein the Kunststoff-Taschenbuch, ed. Saechtling, 25th edition,Hanser-Verlag, Munich, 1992, as well as references cited therein, and inthe Kunststoff-Handbuch, ed. G. Becker and D. Braun, volumes 1 to 11,Hanser-Verlag, Munich, 1966 to 1996. Without being limited to this, thefollowing plastics are to be named by way of example for illustration:polycarbonates (PC), polyoxyalkylenes, polyolefins such as polyethyleneor polypropylene (PP), polyarylene ethers such as polyphenylene ether(PPE), polysulfones, polyurethanes, polylactides, polyamides,vinylaromatic (co)polymers such as polystyrene, impact-modifiedpolystyrene (such as HIPS) or ASA, ABS or AES polymers,halogen-containing polymers, polyesters such as polybutyleneterephthalate (PBT) or polyethylene terephthalate (PET), polymerscontaining imide groups, cellulose esters, poly(meth)acrylates, siliconepolymers and thermoplastic elastomers. Mixtures of different plastics,in particular different thermoplastics, can also be used in the form ofsingle- or multi-phase polymer blends.

In particular embodiments, it is preferred that the coating method isnot non-thermal plasma spraying if the additive is a plastic, inparticular if the additive is a thermosetting plastic or elastomer. Inparticular ones of the above-named embodiments, it is preferred inparticular that the coating method is not non-thermal plasma spraying ifthe additive is a thermosetting plastic.

The poly(meth)acrylates used according to the invention can be presentas homopolymers or as block polymers. Examples are polymethylmethacrylate (PMMA) and copolymers based on methyl methacrylate with upto 40 wt.-% further copolymerizable monomers, such as e.g. n-butylacrylate, t-butyl acrylate or 2-ethylhexyl acrylate.

In particular embodiments, particularly preferred plastic layers aresynthetic resin layers of organofunctional silane and acrylate and/ormethacrylate compound(s). Such coatings according to the invention ofthe particles of the powdered coating material additionally display aparticular stability against mechanical shearing forces, in addition tothe above-named advantages. Furthermore, such coatings protect, forexample, metal pigments against chemicals, strongly aggressive and/orcorrosive media.

The above-named synthetic resin layer can be relatively thin. Forexample, it can have an average layer thickness in a range of from 10 nmto 300 nm, preferably from 15 nm to 220 nm. In particular embodiments,the average layer thickness lies in a range of from 25 to 170 nm, morepreferably in a range of from 35 to 145 nm.

The average layer thickness is determined by measuring the layerthicknesses of at least 30 randomly selected particles by means of SEM.

It is advantageously possible to apply such a synthetic resin layer tothe particles according to the invention in a one-stage method, wherebythe production costs are kept low. In particular preferred embodiments,the organofunctional silane here is in the polyacrylate and/orpolymethacrylate before and/or is incorporated by polymerization.

Furthermore, it is preferred in particular embodiments that the plasticlayer, in particular the synthetic resin layer, has no inorganicnetwork. A pure and homogeneous plastic coating, and in particular apure and homogeneous synthetic resin coating, has proved to besufficient to provide the corrosion stability and chemicals stabilitynecessary under the conditions to be expected of storage, preparation,etc. which precede a use in the one coating method. At the same time,the necessity to remove the inorganic network under the conditions ofthe coating method is avoided.

The above-named organofunctional silane contained in a synthetic resinlayer has at least one functional group which can be reacted chemicallywith an acrylate group and/or methacrylate group of polyacrylate and/orpolymethacrylate. Radically polymerizable organic functional groups haveproved to be very suitable. Preferably, the at least one functionalgroup is selected from the group which consists of acryl, methacryl,vinyl, allyl, ethinyl as well as further organic groups with unsaturatedfunctions. Preferably, the organofunctional silane has at least oneacrylate and/or methacrylate group, because these can be reacted withthe acrylate or methacrylate compounds used to produce the polyacrylateand/or polymethacrylate completely problem-free, accompanied by theformation of a homogeneous plastic layer. The organofunctional silanecan be present as a monomer or also as a polymer. It is important thatthe, monomeric or polymeric, organofunctional silane has at least onefunctional group which allows a chemical reaction with an acrylateand/or methacrylate group. Mixtures of different monomeric and/orpolymeric organofunctional silanes can also be contained in thesynthetic resin layer. For the production of particularly high-qualitysynthetic resin layers it has been shown that there must be ahomogeneous mixing of the organofunctional silane with the polyacrylateand/or polymethacrylate. In contrast, it is not necessary here that theorganofunctional silane is completely reacted chemically with thepolyacrylate and/or polymethacrylate. The chemical reaction betweenorganofunctional silane and polyacrylate and/or polymethacrylate cantherefore be carried out only partially, with the result that forexample only 30% or 40% of the organofunctional silane present, relativeto the total weight of organofunctional silane, is reacted withpolyacrylate and/or polymethacrylate. However, in particularembodiments, it is preferred that at least 60%, further preferably atleast 70%, still further preferably at least 80% of the organofunctionalsilane present, in each case relative to the total weight of theorganofunctional silane, is reacted with polyacrylate and/orpolymethacrylate. Furthermore, at least 90% or at least 95% of theorganofunctional silane is preferably present in a form reacted withpolyacrylate and/or polymethacrylate. Furthermore, it is preferred ifthe reaction is carried out to 100%.

In further preferred embodiments, the polyacrylate and/orpolymethacrylate is built up with or of compounds with several acrylateand/or methacrylate groups. In particular embodiments, it has proved tobe advantageous in particular if the acrylate and/or methacrylatestarting compounds used have two or more acrylate and/or methacrylategroups.

The above-named synthetic resin coatings according to the invention cancontain further monomers and/or polymers in addition to the above-namedacrylate and/or methacrylate compounds. The proportion of acrylateand/or methacrylate compounds including organofunctional silane ispreferably at least 70 wt.-%, further preferably at least 80 wt.-%,still further preferably at least 90 wt.-%, in each case relative to thetotal weight of the synthetic resin coating. According to a preferredvariant, the synthetic resin coating is built up exclusively of acrylateand/or methacrylate compounds and one or more organofunctional silanes,wherein additives such as corrosion inhibitors, colored pigments, dyes,UV stabilizers, etc. or mixtures thereof can also additionally becontained in the synthetic resin coating.

In particular embodiments, it is preferred that the synthetic resinlayers according to the invention with several acrylate groups and/ormethacrylate groups have in each case at least three acrylate and/ormethacrylate groups. Furthermore, these starting compounds canpreferably also have in each case four or five acrylate and/ormethacrylate groups.

In particular embodiments, it is preferred in particular thatpolyfunctional acrylates and/or methacrylates are used for theproduction of the synthetic resin layer according to the invention. Ithas been shown that the synthetic resin layers according to theinvention in which 2 to 4 acrylate and/or methacrylate groups arecontained per acrylate and/or methacrylate starting compoundsurprisingly have an exceptional density and strength, without beingbrittle. 3 acrylate and/or methacrylate groups per acrylate and/ormethacrylate starting compound have proved to be extremely suitable.Such optimized properties have proved to be particularly advantageous inorder to provide a synthetic resin coating which is also suitable forconveying methods in which the particles is led through pipes forexample in the form of an aerosol and in which multiple impacts of theindividual particles on the pipe walls occur.

In particular embodiments, it is preferred in particular that the weightratio of polyacrylate and/or polymethacrylate to organofunctional silaneis 10:1 to 0.5:1.

Furthermore, the weight ratio of polyacrylate and/or polymethacrylate toorganofunctional silane preferably lies in a range of from 7:1 to 1:1.

Examples of suitable difunctional acrylates are: allyl methacrylate,bisphenol A dimethacrylate, 1,3-butanediol dimethacrylate,1,4-butanediol dimethacrylate, ethylene glycol dimethacrylate,1,6-hexanediol diacrylate, 1,6-hexanediol dimethacrylate, diethyleneglycol dimethacrylate, diurethane dimethacrylate, dipropylene glycoldiacrylate, 1,12-dodecanediol dimethacrylate, ethylene glycoldimethacrylate, methacrylic acid anhydride,N,N-methylene-bis-methacrylamide neopentyl glycol dimethacrylate,polyethylene glycol dimethacrylate, polyethylene glycol-200-diacrylate,polyethylene glycol-400-diacrylate, polyethyleneglycol-400-dimethacrylate, tetraethylene glycol diacrylate,tetraethylene glycol dimethacrylate, tricyclodecane dimethanoldiacrylate, tripropylene glycol diacrylate, triethylene glycoldimethacrylate or mixtures thereof.

According to the invention, e.g. pentaerythritol triacrylate,trimethylolpropane triacrylate, trimethylolpropane trimethacrylate,tris-(2-hydroxyethyl)isocyanurate triacrylate, pentaerythritoltetraacrylate, dipentaerythritol pentaacrylate or of mixtures thereofcan be used as higher functional acrylates.

Trifunctional acrylates and/or methacrylates are particularly preferred.

According to the invention for example(methacryloxymethyl)methyldimethoxysilane,methacryloxymethyltrimethoxysilane,(methacryloxymethyl)methyldiethoxysilane,methacryloxymethyltriethoxysilane, 2-acryloxyethylmethyldimethoxysilane,2-methacryloxyethyltrimethoxysilane,3-acryloxypropylmethyldimethoxysilane, 2-acryloxyethyltrimethoxysilane,2-methacryloxyethyltriethoxysilane, 3-acryloxypropyltrimethoxysilane,3-acryloxypropyltripropoxysilane, 3-methacryloxypropyltriethoxysilane,3-methacryloxypropyltrimethoxysilane,3-methacryloxypropyltriacetoxysilane,3-methacryloxypropymethyldimethoxysilane, vinyltrichlorosilane,vinyltrimethoxysilane vinyldimethoxymethylsilane, vinyltriethoxysilane,vinyltris(2-methoxyethoxy)silane, vinyltriacetoxysilane or mixturesthereof can be used as organofunctional silanes. Acrylate- and/ormethacrylate-functional silanes are particularly preferred. Inparticular embodiments, 2-methacryloxyethyltrimethoxysilane,2-methacryloxyethyltriethoxysilane, 3-methacryloxypropyltriethoxysilane,3-methacryloxypropyltrimethoxysilane,(methacryloxymethyl)methyldimethoxysilane, vinyltrimethoxysilane ormixtures thereof in particular have proved to be particularly suitableorganofunctional silanes.

It has surprisingly been shown that, with the powdered coating materialsaccording to the invention, even very thin layer thicknesses of theabove-named synthetic resin layer are sufficient to guarantee a highchemical and mechanical stability of the particles according to theinvention. At the same time, the use of such thin layers makes itpossible, even at low temperatures and with only a short residence inthe combustion flame or plasma flame, for such a coating to be removedor at least loosened to such an extent that the material used for thecoating is not contained as an impurity in the coating or is present atleast in such a small quantity that there is no noticeable impairment ofthe properties of the coating produced by means of the coating method.In particular embodiments, however, it is preferred in particular thatthe layer thickness and the composition of the synthetic resin layer areselected such that no detectable residues of the synthetic resin layerare contained in the coating produced in the coating method.

The further plastics named above by way of example are known to a personskilled in the art and can be selected on the basis of the inventiondisclosed herein in order to provide the effect according to theinvention.

Examples of polycarbonates and the production thereof can be found in DE1 300 266 B1 (interfacial polycondensation) or DE 14 95 730 A1 (reactionof biphenyl carbonate with bisphenols).

In the case of polyoxyalkylene homo- or copolymers, the polymer mainchain has at least 50 mol.-% recurring units of —CH₂O—. A particularexample of this plastic group is constituted by (co)polyoxymethylenes(POM). The homopolymers can be produced, preferably catalytically, forexample by polymerization of formaldehyde or trioxane.

Examples of the above-named polyolefins are polyethylene andpolypropylene as well as copolymers based on ethylene or propylene,optionally also with higher α-olefins. The term “polyolefin” within themeaning of the present invention also comprises in particularethylene-propylene elastomers and ethylene-propylene terpolymers.

Examples of the above-named polyarylene ethers are polyarylene ethersper se, polyarylene ether sulfides, polyarylene ether sulfones andpolyarylene ether ketones. The arylene groups here can be the same ordifferent, and independently of each other can be for example anaromatic radical with 6 to 18 C atoms. Arylene radicals named by way ofexample are phenylene, bisphenylene, terphenylene, 1,5-naphthylene,1,6-naphthylene, 1,5-anthrylene, 9,10-anthrylene or 2,6-anthrylene.Specific information in respect of the production of polyarylene ethersulfones is found for example in EP 113 112 A1 and EP 135 130 A2.

In particular embodiments, it is preferred in particular to usecopolymers or block copolymers based on lactic acid and further monomersas polylactides.

The term “polyamides” within the meaning of the present inventioncomprises for example polyetheramides such as polyether block amides,polycaprolactams, polycapryllactams, polylaurolactams and polyamideswhich are obtained by reacting dicarboxylic acids with diamines.Disclosures in respect of the production of polyetheramides are foundfor example in U.S. Pat. No. 2,071,250, U.S. Pat. No. 2,071,251, U.S.Pat. No. 2,130,523, U.S. Pat. No. 2,130,948, U.S. Pat. No. 2,241,322,U.S. Pat. No. 2,312,966, U.S. Pat. No. 2,512,606 and U.S. Pat. No.3,393,210. Dicarboxylic acids which can be reacted with the above-nameddiamines are for example alkanedicarboxylic acids with 6 to 12, inparticular 6 to 10 carbon atoms and aromatic dicarboxylic acids.Suitable diamines are for example alkanediamines with 6 to 12, inparticular 6 to 8 carbon atoms, as well as m-xylylenediamine,di-(4-aminophenyl)methane, di-(4-aminocyclohexyl)methane,2,2-di-(4-aminophenyl)propane or 2,2-di-(4-aminocyclohexyl)propane.

Examples of vinylaromatic (co)polymers known to a person skilled in theart are polystyrene, styrene-acrytnitrile copolymers (SAN),impact-modified polystyrene (HIPS=High Impact Polystyrene) and ASA, ABSand AES polymers (ASA=acrylonitrile-styrene-acrylester,ABS=acrylonitrile-butadiene-styrene, AES=acrylonitrile-EPDMrubber-styrene). Examples of disclosures of the production of suchplastics are found in EP-A-302 485, DE 197 28 629 A1, EP 99 532 A2, U.S.Pat. No. 3,055,859 and U.S. Pat. No. 4,224,419.

Examples of halogen-containing polymers are polymers of vinyl chloride,in particular polyvinyl chloride (PVC) such as hard PVC and soft PVC,and copolymers of vinyl chloride such as PVC-U molding compounds.

Polyester plastics which can be selected according to the invention arelikewise known per se and described in the literature. The polyesterscan be produced by reacting aromatic dicarboxylic acids, esters thereofor other ester-forming derivatives of same with aliphatic dihydroxycompounds in a manner known per se. In particular embodiments,naphthalene dicarboxylic acid, terephthalic acid and isophthalic acid ormixtures thereof are used as dicarboxylic acids. Up to 10 mol.-% of thearomatic dicarboxylic acids can be replaced by aliphatic orcycloaliphatic dicarboxylic acids such as adipic acid, azelaic acid,sebacic acid, dodecane diacids and cyclohexane dicarboxylic acids.Examples of aliphatic dihydroxy compounds are diols with 2 to 6 carbonatoms, in particular 1,2-ethanediol, 1,4-butanediol, 1,6-hexanediol,1,4-hexanediol, 1,4-cyclohexanediol and neopentyl glycol or mixturesthereof.

Examples of the polymers containing imide groups are polyimides,polyetherimides, and polyamide-imides. Such polymers are described forexample in Römpp Chemie Lexikon, CD-ROM version 1.0, Thieme VerlagStuttgart 1995.

Furthermore, for example fluorine-containing polymers such aspolytetrafluoroethylene (PTFE), tetrafluoroethylene-perfluoropropylenecopolymers (FEP), copolymers of tetrafluoroethylene with perfluoroalkylvinyl ether, ethylene-tetrafluoroethylene copolymers (ETFE),polyvinylidene fluoride (PVDF), polyvinyl fluoride (PVF),polychlorotrifluoroethylene (PCTFE) and ethylene-chlorotrifluoroethylenecopolymers (ECTFE) can be used.

The above-named thermoplastic elastomers (TPE) are characterized in thatthey can be processed like thermoplastics but have rubber-elasticproperties. More detailed information is found for example in G. Holdenet al., Thermoplastic Elastomers, 2^(nd) edition, Hanser Verlag, Munich1996. Examples are thermoplastic polyurethane elastomers (TPE-U or TPU),styrene oligoblock copolymers (TPE-S) such as SBS(styrene-butadiene-styrene-oxy block copolymer) and SEES(styrene-ethylene-butylene-styrene block copolymer, obtainable byhydrogenation of SBS), thermoplastic polyolefin elastomers (TPE-O),thermoplastic polyester elastomers (TPE-E), thermoplastic polyamideelastomers (TPE-A) and thermoplastic vulcanizates (TPE-V).

In particular embodiments, it is preferred that the polymers used ascoating additives have a molecular weight of at most 200,000, preferablyof at most 170,000, more preferably of at most 150,000 and still morepreferably at most 130,000. In particular ones of the above-namedembodiments, it is preferred in particular that the compounds used ascoating additives have a molecular weight of at most 110,000, preferablyof at most 90,000, more preferably of at most 70,000 and still morepreferably of at most 50,000.

The above-named carboxylic acids used as coating additive also comprisein particular dicarboxylic acids, tricarboxylic acids andtetracarboxylic acids in particular embodiments. Examples ofdicarboxylic acids are succinic acid, glutaric acid, adipic acid,pimelic acid, suberic acid, azelaic acid and sebacic acid.

In particular preferred embodiments, the above-named carboxylic acidderivatives are directed in particular towards carboxylic acid esters.

Examples of the above-named fatty acids are capric acid, undecanoicacid, lauric acid, tridecanoic acid, myristic acid, pentadecanoic acid,palmitic acid, margaric acid, nonadecanoic acid, arachidic acid, behenicacid, lignoceric acid, cerotic acid, melissic acid, undecylenic acid,palmitoleic acid, elaidic acid, vaccenic acid, eicosenoic acid, cetoleicacid, erucic acid, nervonic acid, sorbic acid, linoleic acid, linolenicacid, eleostearic acid, arachidonic acid, timnodonic acid, clupanodonicacid, docosahexaenoic acid, stearic acid and oleic acid. In particularquite particularly preferred embodiments of the present invention, thecoating additives comprise no stearic acid or oleic acid, preferably nosaturated or unsaturated C18 carboxylic acids, more preferably nosaturated or unsaturated C14 to C18 carboxylic acids, still morepreferably no saturated or unsaturated C12 to C18 carboxylic acids andmost preferably no saturated or unsaturated C10 to C20 carboxylic acids.The term “C” followed by a number relates within the meaning of thepresent invention to the carbon atoms contained in a molecule ormolecule constituent, wherein the number expresses the quantity ofcarbon atoms.

The above-named phosphonic acids are expressed by Formula (I):

(X)_(m)P(=0)Y_(n)R_((3-m))  (I),

wherein m is 0, 1 or 2, n is 0 or 1, X can be the same or different andis hydrogen, hydroxy, halogen or —NR′₂, R′ can be the same or differentand is hydrogen, a substituted or unsubstituted C1-C9 alkyl group or asubstituted or unsubstituted aryl group, Y can be the same or differentand is —O—, —S—, —NH— or —NR— and R can be the same or different and isselected from the group consisting of C1-C30 alkyl groups, C2-C30alkenyl groups, C2-C30 alkinyl groups, C5-C30 aryl groups, C6-C30arylalkyl groups, C4-C30 heteroaryl groups, C5-C30 heteroarylalkylgroups, C3-C30 cycloalkyl groups, C4-C30 cycloalkylalkyl groups, C2-C30heterocycloalkyl groups, C3-C30 heterocycloalkylalkyl groups, C1-C30ester groups, C1-C30 alkyl ether groups, C1-C30 cycloalkyl ether groups,C1-C30 cycloalkenyl ether groups, C6-C30 aryl ether groups, C7-C30arylalkyl ether groups, wherein the above-named groups can besubstituted or unsubstituted and optionally straight-chained orbranched.

The term “substituted” within the meaning of the present inventiondescribes that at least one hydrogen atom of the relevant group by ahalogen, hydroxy, cyano, C1-C8 alkyl, C2-C8 alkenyl, C2-C8 alkinyl,C1-C5 alkanoyl, C3-C8 cycloalkyl, heterocyclic, aryl, heteroaryl, C1-C7alkylcarbonyl, C1-C7 alkoxy, C2-C7 alkenyloxy, C2-C7 alkinyloxy,aryloxy, acyl, C1-C7 acryloxy, C1-C7 methacryloxy, C1-C7 epoxy, C1-C7vinyl, C1-C5 alkoxycarbonyl, aroyl, aminocarbonyl, alkylaminocarbonyl,dialkylaminocarbonyl, amincarbonyloxy, C1-C7 alkylaminocarbonyloxy,C1-C7 dialkylamincarbonyloxy, C1-C7 alkanoylamine, C1-C7alkoxycarbonylamine, C1-C7 alkylsulfonylamine, aminosulfonyl, C1-C7alkylaminosulfonyl, C1-C7 dialkylaminsulfonyl, carboxy, cyano,trifluoromethyl, trifluoromethoxy, nitro, sulfonic acid, phosphoricacid, amine; amide; the nitrogen atom optionally, independently of eachother, substituted once or twice with C1-C5 alkyl or aryl groups;ureido; the nitrogen atoms optionally, independently of each other,substituted once or twice with C1-C5 alkyl or aryl groups; or C1-C5alkylthio group.

The terms “cycloalkyl group” and “heterocycloalkyl group” within themeaning of the present invention comprise saturated, partially saturatedand unsaturated systems, apart from aromatic systems, which are called“aryl groups” or “heteroaryl groups”.

The term “alkyl” within the meaning of the present invention, unlessotherwise indicated, preferably represents straight or branched C1 toC27, more preferably straight or branched C1 to C25 and still morepreferably straight or branched C1 to C20 carbon chains. The terms“alkenyl” and “alkinyl” within the meaning of the present invention,unless otherwise indicated, preferably represent straight or branched C2to C27, more preferably straight or branched C2 to C25 and still morepreferably straight or branched C2 to C20 carbon chains. The term “aryl”within the meaning of the present invention represents aromatic carbonrings, preferably aromatic carbon rings with at most 7 carbon atoms,more preferably the phenyl ring, wherein the above-named aromatic carbonrings can be a constituent of a condensed ring system. Examples of arylgroups are phenyl, hydroxyphenyl, biphenyl and naphthyl. The term“heteroaryl” within the meaning of the present invention representsaromatic rings, in which a carbon atom of an analogous aryl ring hasformally been replaced by a heteroatom, preferably by an atom selectedfrom the group consisting of O, S and N.

The above-named silanes are characterized by a structure according toFormula (II):

R_(p)SiX_((4-p))  (II),

wherein p is 0, 1, 2 or 3, X can be the same or different and ishydrogen, hydroxy, halogen or —NR′₂, R′ can be the same or different andis hydrogen, a substituted or unsubstituted C1-C9 alkyl group or asubstituted or unsubstituted aryl group and R can be the same ordifferent and is selected from the group consisting of C1-C30 alkylgroups, C2-C30 alkenyl groups, C2-C30 alkinyl groups, C5-C30 arylgroups, C6-C30 arylalkyl groups, C4-C30 heteroaryl groups, C5-C30heteroarylalkyl groups, C3-C30 cycloalkyl groups, C4-C30 cycloalkylalkylgroups, C2-C30 heterocycloalkyl groups, C3-C30 heterocycloalkylalkylgroups, C1-C30 ester groups, C1-C30 alkyl ether groups, C1-C30cycloalkyl ether groups, C1-C30 cycloalkenyl ether groups, C6-C30 arylether groups, C7-C30 arylalkyl ether groups, wherein the above-namedgroups can be substituted or unsubstituted and optionallystraight-chained or branched.

The coating additive can be bound for example chemically or physicallyto the surface of the particles of the powdered coating material. It isnot necessary here that an unbroken surface coverage of the particles iscarried out, even if this is preferred in particular embodiments of thepresent invention.

In particular embodiments, it is preferred that the coating additivesare bound as weakly as possible to the surface of the particles of thepowdered coating material.

For example, in particular ones of the above-named embodiments, it ispreferred that the coating additives used according to the inventioncarry no functional group. The term “functional group” within themeaning of the present invention denotes molecular groups in moleculeswhich decisively influence the substance properties and the reactionbehavior of the molecules. Examples of such functional groups are:carboxylic acid groups, sulfonic acid groups, phosphoric acid groups,silane groups, carbonyl groups, hydroxyl groups, amine groups, hydrazinegroups, halogen groups and nitro groups.

In particular other embodiments, in contrast, it is preferred that thecoating additives cannot be removed from the surface too easily, forexample as a result of friction. In particular ones of the above-namedembodiments, it is preferred in particular that the coating additivesused according to the invention carry at least one functional group,preferably at least two functional groups, more preferably at leastthree functional groups.

Additionally, it was surprisingly found that the use of the powderedcoating material according to the invention with a surface coverageaccording to the invention can also be used coating materials with anunexpectedly high melting point. Without being understood as limitingthe invention, the inventors are of the view that the more uniformconveying of the particles with reduced tendency to agglomerate allowsthe individual particles to strike the substrate surface and the kineticenergy present to be able to be utilized fully to shape the particle. Inthe case of a non-uniform, thus localized, application of agglomerates,some of the kinetic energy is possibly used up by the breakup of theagglomerate and particles that strike later are cushioned by coatingmaterial already present at this site, but not yet solidified. If thepowdered coating material is passed through a flame beforehand, thethermal energy is furthermore probably better transferred to theparticles in the case of uniform fed-in particles without agglomerates.

For example, in particular embodiments powdered coating materialscovered according to the invention with at least one coating additivecan also be used to produce homogeneous layers if the melting point,measured in [K], of the coating material is up to 50%, preferably up to60%, more preferably up to 65% and still more preferably up to 70% ofthe temperature, measured in [K], of the medium used in the coatingmethod directed onto the substrate, for example the gas stream, thecombustion flame and/or the plasma flame. In particular ones of theabove-named embodiments furthermore powdered coating materials coveredaccording to the invention with at least one coating additive can alsobe used to produce homogeneous layers if the melting point, measured in[K], of the coating material is up to 75%, preferably up to 80%, morepreferably up to 85% and still more preferably up to 90% of thetemperature, measured in [K], of the medium used in the coating methoddirected onto the substrate, for example the gas stream, the combustionflame and/or the plasma flame. The above-named percentages relate to theratio of the melting temperature of the coating material to thetemperature of the gas stream in cold gas spraying, the combustion flamein flame spraying and high-speed flame spraying or the plasma flame innon-thermal or thermal plasma spraying in [K]. The thus-obtained coatinghas only a few free particle or grain structures, preferably none. Theabove-named homogeneous layers are characterized in that the producedlayers have less than 10%, preferably less than 5%, more preferably lessthan 3%, still more preferably less than 1% and most preferably lessthan 0.1% cavities. In particular, it is preferred that no cavities atall are recognizable. The above-named term “cavity” within the meaningof the present invention describes the proportion of holes, incorporatedin the coating, on the two-dimensional surface of a cross-section of thecoated substrate, relative to the coating contained in thetwo-dimensional surface. A determination of this proportion is carriedout by means of SEM at 30 randomly selected sites on the coating,wherein for example a length of 100 μm of the substrate coating isexamined.

It was surprisingly found that, through the use of the powdered coatingmaterial according to the invention, homogeneous coatings could also beproduced from materials which have a strong tendency to formagglomerates for example because of their particle-size distributionsand which tend to form non-homogeneous coatings as a result of a lack ofbreakup of the above-named agglomerates.

The size distribution of the particles is preferably determined by meansof laser granulometry. In this method, the particles can be measured inthe form of a powder. The scattering of the irradiated laser light isdetected in different spatial directions and evaluated according to theFraunhofer diffraction theory. The particles are treated computationallyas spheres. Thus, the determined diameters always relate to theequivalent spherical diameter determined over all spatial directions,irrespective of the actual shape of the particles. The size distributionis determined, calculated in the form of a volume average relative tothe equivalent spherical diameter. This volume-averaged sizedistribution can be represented as a cumulative frequency distribution.The cumulative frequency distribution is characterized in a simplifiedmanner by different characteristic values, for example the D₁₀, D₅₀ orD₉₀ value.

The measurements can be carried out for example with the particle-sizeanalyzer HELOS from Sympatec GmbH, Clausthal-Zellerfeld, Germany. Here,a dry powder can be dispersed using a dispersing unit of the Rodos T4.1type at a primary pressure of for example 4 bar. Alternatively, a sizedistribution curve of the particles can be measured, for example, with adevice from Quantachrome (device: Cilas 1064) according to themanufacturers instructions. For this, 1.5 g of the powdered coatingmaterial is suspended in approx. 100 ml isopropanol, treated for 300seconds in an ultrasound bath (device: Sonorex IK 52, Bandelin) and thenintroduced by means of a Pasteur pipette into the sample preparationcell of the measuring device and measured several times. The resultantaverage values are formed from the individual measurement results. Thescattered light signals are evaluated according to the Fraunhofermethod.

In particular embodiments of the invention, it is preferred that thepowdered coating material has a particle-size distribution with a D₅₀value of at most 53 μm, preferably at most 51 μm, more preferably atmost 50 μm and still more preferably at most 49 μm. In particular onesof the above-named embodiments, it is preferred in particular that thepowdered coating material has a particle-size distribution with a D₅₀value of at most 48 μm, preferably at most 47 μm, more preferably atmost 46 μm and still more preferably at most 45 μm.

The term “D₅₀” within the meaning of the present invention denotes theparticle size at which 50% of the above-named particle-size distributionvolume-averaged by means of laser granulometry lies below the indicatedvalue. The measurements can be carried out for example according to theabove-named measurement method with a particle-size analyzer HELOS fromSympatec GmbH, Clausthal-Zellerfeld, Germany.

In particular embodiments of the invention, it is preferred inparticular that the powdered coating material has a particle-sizedistribution with a D₅₀ value of at least 1.5 μm, preferably at least 2μm, more preferably at least 4 μm and still more preferably at least 6μm. In particular ones of the above-named embodiments, it is preferredin particular that the powdered coating material has a particle-sizedistribution with a D₅₀ value of at least 7 μm, preferably at least 9μm, more preferably at least 11 μm and still more preferably at least 13μm.

In particular embodiments, it is furthermore preferred that the powderhas a particle-size distribution with a D₅₀ value from a range of from1.5 to 53 μm, preferably from a range of from 2 to 51 μm, morepreferably from a range of from 4 to 50 μm and still more preferablyfrom a range of from 6 to 49 μm. In particular ones of the above-namedembodiments, it is preferred in particular that the powder has aparticle-size distribution with a D₅₀ value from a range of from 7 to 48μm, preferably from a range of from 9 to 47 μm, more preferably from arange of from 11 to 46 μm and still more preferably from a range of from13 to 45 μm.

In other embodiments, it is preferred for example that the powder has aparticle-size distribution with a D₅₀ value from a range of from 1.5 to45 μm, preferably from a range of from 2 to 43 μm, more preferably froma range of from 2.5 to 41 μm and still more preferably from a range offrom 3 to 40 μm. In particular ones of the above-named embodiments, itis preferred in particular that the powder has a particle-sizedistribution with a D₅₀ value from a range of from 3.5 to 38 μm,preferably from a range of from 4 to 36 μm, more preferably from a rangeof from 4.5 to 34 μm and still more preferably from a range of from 5 to32 μm.

In still other embodiments, in contrast, it is preferred for examplethat the powder has a particle-size distribution with a D₅₀ value from arange of from 9 to 53 μm, preferably from a range of from 12 to 51 μm,more preferably from a range of from 15 to 50 μm, still more preferablyfrom a range of from 17 to 49 μm. In particular ones of the above-namedembodiments, it is preferred in particular that the powder has aparticle-size distribution with a D₅₀ value from a range of from 19 to48 μm, preferably from a range of from 21 to 47 μm, more preferably froma range of from 23 to 46 μm and still more preferably from a range offrom 25 to 45 μm.

In further particular embodiments of the invention, it is preferred thatthe powdered coating material has a particle-size distribution with aD₉₀ value of at most 103 μm, preferably at most 99 μm, more preferablyat most 95 μm, still more preferably at most 91 μm and most preferablyat most 87 μm. In particular ones of the above-named embodiments, it ispreferred in particular that the powdered coating material has a D₉₀value of at most 83 μm, preferably at most 79 μm, more preferably atmost 75 μm and still more preferably at most 71 μm.

The term “D₉₀” within the meaning of the present invention denotes theparticle size at which 90% of the above-named particle-size distributionvolume-averaged by means of laser granulometry lies below the indicatedvalue. The measurements can be carried out for example according to theabove-named measurement method with a particle-size analyzer HELOS fromSympatec GmbH, Clausthal-Zellerfeld, Germany.

In particular embodiments, it is therefore preferred that the powderedcoating material has a particle-size distribution with a D₉₀ value of atleast 9 μm, preferably at least 11 μm, more preferably at least 13 μmand still more preferably at least 15 μm. In particular ones of theabove-named embodiments, it is preferred in particular that the powderedcoating material has a particle-size distribution with a D₉₀ value of atleast 17 μm, preferably at least 19 μm, more preferably at least 21 μmand still more preferably at least 22 μm.

According to particular preferred embodiments, the powdered coatingmaterials have a particle-size distribution with a D₉₀ value from arange of from 42 to 103 μm, preferably from a range of from 45 to 99 μm,more preferably from a range of from 48 to 95 μm and still morepreferably from a range of from 50 to 91 μm. In particular ones of theabove-named embodiments, it is preferred in particular that the powderedcoating material has a D₉₀ value from a range of from 52 to 87 μm,preferably from a range of from 54 to 81 μm, more preferably from arange of from 56 to 75 μm and still more preferably from a range of from57 to 71 μm.

In further particular embodiments, it is preferred that the powderedcoating material has a particle-size distribution with a D₁₀ value of atmost 5 μm, preferably at most 4 μm, more preferably at most 3 μm andstill more preferably at most 2.5 μm. In particular ones of theabove-named embodiments, it is preferred in particular that the powderedcoating material has a particle-size distribution with a D₁₀ value of atmost 2.2 μm, preferably at most 2 μm, more preferably at most 1.8 μm andstill more preferably at most 1.7 μm.

The term “D₁₀” within the meaning of the present invention denotes theparticle size at which 10% of the above-named particle-size distributionvolume-averaged by means of laser granulometry lies below the indicatedvalue. The measurements can be carried out for example according to theabove-named measurement method with a particle-size analyzer HELOS fromSympatec GmbH, Clausthal-Zellerfeld, Germany.

On the other hand, the powdered coating materials according to theinvention with a high fines proportion also still have a strong tendencyto form fine dusts, which makes the handling of corresponding powdersmuch more difficult. In particular embodiments, therefore, it ispreferred that the powdered coating material according to the inventionhas a particle-size distribution with a D₁₀ value of at least 0.2 μm,preferably at least 0.4 μm, more preferably at least 0.5 μm and stillmore preferably at least 0.6 μm. In particular ones of the above-namedembodiments, it is preferred in particular that the powdered coatingmaterial according to the invention has a particle-size distributionwith a D₁₀ value of at least 0.7 μm, preferably 0.8 μm, more preferably0.9 μm and still more preferably at least 1.0 μm.

In particular preferred embodiments, the powdered coating materialaccording to the invention is characterized in that it have aparticle-size distribution with a D₁₀ value from a range of from atleast 0.2 to 5 μm, preferably at least 0.4 to 4 μm, more preferably froma range of from 0.5 to 3 μm and still more preferably from a range offrom 0.6 to 2.5 μm. In particular ones of the above-named embodiments,it is preferred in particular that the powdered coating materialaccording to the invention has a particle-size distribution with a D₁₀value from a range of from 0.7 to 2.2 μm, preferably from a range offrom 0.8 to 2.1 μm, more preferably from a range of from 0.9 to 2.0 μmand still more preferably from a range of from 1.0 to 1.9 μm.

For example, in particular embodiments, it is preferred in particularthat the powdered coating material has a particle-size distribution witha D₁₀ value of from 3.7 to 26 μm, a D₅₀ value of from 6 to 49 μm and aD₉₀ value of from 12 to 86 μm. In particular ones of the above-namedembodiments, it is particularly preferred that the powdered coatingmaterial has a particle-size distribution with a D₁₀ value of from 5.8to 26 μm, a D₅₀ value of from 11 to 46 μm and a D₉₀ value of from 16 to83 μm. In particular ones of the above-named embodiments, it is stillmore preferred that the powdered coating material has a particle-sizedistribution with a D₁₀ value of from 9 to 19 μm, a D₅₀ value of from 16to 35 μm and a D₉₀ value of from 23 to 72 μm.

In further particular embodiments, it is preferred for example that thepowdered coating material has a particle-size distribution with a D₁₀value of from 0.8 to 28 μm, a D₅₀ value of from 1.5 to 45 μm and a D₉₀value of from 2.5 to 81 μm. In particular ones of the above-namedembodiments, it is particularly preferred that the powdered coatingmaterial has a particle-size distribution with a D₁₀ value of from 2.2to 22 μm, a D₅₀ value of from 4 to 36 μm and a D₉₀ value of from 4 to 62μm. In particular ones of the above-named embodiments, it is still morepreferred that the powdered coating material has a particle-sizedistribution with a D₁₀ value of from 2.8 to 17 μm, a D₅₀ value of from6 to 28 μm and a D₉₀ value of from 9 to 49 μm.

In further particular embodiments, it is preferred for example that thepowdered coating material has a particle-size distribution with a D₁₀value of from 4.8 to 29 μm, a D₅₀ value of from 9 to 53 μm and a D₉₀value of from 13 to 97 μm. In particular ones of the above-namedembodiments, it is particularly preferred that the powdered coatingmaterial has a particle-size distribution with a D₁₀ value of from 12 to26 μm, a D₅₀ value of from 23 to 46 μm and a D₉₀ value of from 35 to 87μm. In particular ones of the above-named embodiments, it is still morepreferred that the powdered coating material has a particle-sizedistribution with a D₁₀ value of from 15 to 24 μm, a D₅₀ value of from28 to 44 μm and a D₉₀ value of from 41 to 78 μm.

Furthermore, it was observed that the conveyability of the powderedcoating material according to the invention is dependent on the width ofthe particle-size distribution. This width can be calculated byindicating the so-called span value, which is defined as follows:

${Span} = \frac{D_{90} - D_{10}}{D_{50}}$

The inventors have found that in particular embodiments, for example, astill more uniform conveyability of the powdered coating material isachieved through the use of a powdered coating material with a smallerspan, which further simplifies the formation of a more homogeneous andhigher-quality layer. In particular embodiments, therefore, it ispreferred that the span of the powdered coating material is at most 2.9,preferably at most 2.6, more preferably at most 2.4 and still morepreferably at most 2.1. In particular ones of the above-namedembodiments, it is preferred in particular that the span of the powderedcoating material is at most 1.9, preferably at most 1.8, more preferablyat most 1.7 and still more preferably at most 1.6.

On the other hand, the inventors have found that a very narrow span isnot necessarily required to provide the sought conveyability, whichmakes the production of the powdered coating material easier. Inparticular embodiments, therefore, it is preferred that the span valueof the powdered coating material is at least 0.4, preferably at least0.5, more preferably at least 0.6 and still more preferably at least0.7. In particular embodiments, it is preferred in particular that thespan value of the powdered coating material is at least 0.8, preferablyat least 0.9, more preferably at least 1.0 and still more preferably atleast 1.1.

On the basis of the teaching disclosed herein, a person skilled in theart can select any combination, in particular of the above-named limitvalues of the span value, in order to provide the desired combination ofproperties. In particular embodiments, it is preferred for example thatthe powdered coating material has a span value from a range of from 0.4to 2.9, preferably from a range of from 0.5 to 2.6, more preferably froma range of from 0.6 to 2.4 and still more preferably from a range offrom 0.7 to 2.1. In particular ones of the above-named embodiments, itis preferred in particular that the powdered coating material has a spanvalue from a range of from 0.8 to 1.9, preferably from a range of from0.9 to 1.8, more preferably from a range of from 1.0 to 1.7 and stillmore preferably from a range of from 1.1 to 1.6.

A person skilled in the art is aware that, on the basis of the teachingdisclosed herein, particular combinations of the span limit values orvalue ranges with the above-named preferred D₅₀ value ranges arepreferred depending on the desired combination of advantages. Inparticular preferred embodiments, the powdered coating material has forexample a particle-size distribution with a span from a range of from0.4 to 2.9 and a D₅₀ value from a range of from 1.5 to 53 μm, preferablyfrom a range of from 2 to 51 μm, more preferably from a range of from 4to 50 μm, still more preferably from a range of from 6 to 49 μm and mostpreferably from a range of from 7 to 48 μm. In particular preferred onesof the above-named embodiments, the powdered coating material has aparticle-size distribution with a span from a range of from 0.5 to 2.6and a D₅₀ value from a range of from 1.5 to 53 μm, preferably from arange of from 2 to 51 μm, more preferably from a range of from 4 to 50μm, still more preferably from a range of from 6 to 49 μm and mostpreferably from a range of from 7 to 48 μm. In particular furtherpreferred embodiments, the powdered coating material has a particle-sizedistribution with a span from a range of from 0.6 to 2.4 and a D₅₀ valuefrom a range of from 1.5 to 53 μm, preferably from a range of from 2 to51 μm, more preferably from a range of from 4 to 50 μm, still morepreferably from a range of from 6 to 49 μm and most preferably from arange of from 7 to 48 μm. In particular still further preferredembodiments, the powdered coating material has a particle-sizedistribution with a span from a range of from 0.7 to 2.1 and a D₅₀ valuefrom a range of from 1.5 to 53 μm, preferably from a range of from 2 to51 μm, more preferably from a range of from 4 to 50 μm, still morepreferably from a range of from 6 to 49 μm and most preferably from arange of from 7 to 48 μm.

Furthermore, it was found that the density of the powdered coatingmaterial can influence the conveying of such powders in the form of anaerosol. Without being understood as limiting the invention, theinventors are of the view that the differences in inertia of particlesthat are the same size but have different densities lead to a differentbehavior of the aerosol streams of powdered coating materials withidentical particle-size distribution. It can therefore prove to bedifficult to transfer conveying methods which have been optimized for aspecific D₅₀ to powdered coating materials with other densities. Inparticular embodiments, therefore, it is preferred that the upper limitof the span value is corrected dependent on the density of the powderedcoating material used.

${Span}_{UC} = {{Span}_{U} \cdot \left( \frac{\rho_{Alu}}{\rho_{X}} \right)^{\frac{1}{3}}}$

Here, Span_(UC) is the corrected upper span value, Span_(U) is the upperspan value, ρ_(Alu) is the density of aluminum (2.7 g/cm³) and ρ_(X) isthe density of the powdered coating material used. However, it wasfurthermore found that the differences in the case of powdered coatingmaterials with a lower density than aluminum are only slight, and aselection, optimized in this respect, of the powdered coating materialdoes not result in a noticeable improvement in the conveyability. Apowdered coating material with an uncorrected upper span value istherefore used for powdered coating materials with a density lower thanthe density of aluminum.

Coating methods that can be used according to the invention are known toa person skilled in the art under the names cold gas spraying, thermalplasma spraying, non-thermal plasma spraying, flame spraying andhigh-speed flame spraying.

Cold gas spraying is characterized in that the powder to be applied isnot melted in the gas jet, but the particles are greatly acceleratedand, as a result of their kinetic energy, form a coating on the surfaceof the substrate. Here, various gases known to a person skilled in theart can be used as carrier gas, such as nitrogen, helium, argon, air,krypton, neon, xenon, carbon dioxide, oxygen or mixtures thereof. Inparticular variants, it is preferred in particular that air, helium ormixtures thereof are used as gas.

Gas speeds of up to 3000 m/s are achieved through a controlled expansionof the above-named gases in a corresponding nozzle. The particles can beaccelerated here to up to 2000 m/s. However, in particular variants ofcold gas spraying, it is preferred that the particles achieve speeds forexample of between 300 m/s and 1600 m/s, preferably between 1000 m/s and1600 m/s, more preferably between 1250 m/s and 1600 m/s.

A disadvantage is, for example, the strong generation of noise which isbrought about by the high speeds of the gas streams used.

In flame spraying, for example, a powder is converted to the liquid orplastic state by means of a flame and then applied to a substrate ascoating. Here, e.g. a mixture of oxygen and a combustible gas such asacetylene or hydrogen is combusted. In particular variants of flamespraying, some of the oxygen is used to transport the powdered coatingmaterial into the combustion flame. The particles achieve speeds ofbetween 24 and 31 m/s in customary variants of this method.

Similarly to flame spraying, in high-speed flame spraying, for example,a powder is also converted to the liquid or plastic state by means of aflame. However, the particles are accelerated to significantly higherspeeds compared with the above-named method. In specific examples of theabove-named method, for example, a speed of the gas stream of from 1220to 1525 m/s with a speed of the particles of from approx. 550 to 795 m/sis named. In further variants of this method, however, gas speeds ofover 2000 m/s are also achieved. In general, in customary variants ofthe previous method, it is preferred that the speed of the flame liesbetween 1000 and 2500 m/s. Furthermore, in customary variants, it ispreferred that the flame temperature lies between 2200° C. and 3000° C.The temperature of the flame is thus comparable to the temperature inflame spraying. This is achieved by combusting the gases under apressure of from approx. 515 to 621 kPa, followed by expansion of thecombustion gases in a nozzle. In general, the view is taken thatcoatings produced here have a higher density than, for example, coatingsobtained by the flame spraying method.

Detonation/explosive flame spraying can be viewed as a subtype ofhigh-speed flame spraying. Here, the powdered coating material isstrongly accelerated by repeated detonations of a gas mixture such asacetylene/oxygen, wherein for example particle speeds of approx. 730 m/sare achieved. The detonation frequency of the method here becomes forexample between approx. 4 and 10 Hz. In variants such as the so-calledhigh frequency gas detonation spraying, however, detonation frequenciesof around approx. 100 Hz are also chosen.

The layers obtained are usually supposed to have a particularly highhardness, strength, density and good binding to the substrate surface. Adisadvantage in the above-named methods is the increased safety costs,as well as for example the high noise load because of the high gasspeeds.

In thermal plasma spraying, for example, a direct current arc furnace ispassed through by a primary gas such as argon at a speed of 40 l/min anda secondary gas such as hydrogen at a speed of 2.5 l/min, wherein athermal plasma is generated. Then, for example, 40 g/min of the powderedcoating material is fed in with the aid of a carrier gas stream, whichis passed into the plasma flame at a speed of 4 l/min. In usual variantsof thermal plasma spraying, the conveying rate of the powdered coatingmaterial is between 5 g/min and 60 g/min, more preferably between 10g/min and 40 g/min.

In particular variants of the method, it is preferred to use argon,helium or mixtures thereof as ionizable gas. The whole gas stream isfurthermore preferably 30 to 150 SLPM (standard liters per minute) inparticular variants. The electrical power used to ionize the gas stream,without the heat energy dissipated as a result of cooling, can beselected for example between 5 and 100 kW, preferably between 40 and 80kW. Here, plasma temperatures of between 4000 and a few 10000 K can beachieved.

In non-thermal plasma spraying, a non-thermal plasma is used to activatethe powdered coating material. The plasma used here is generated forexample with a barrier discharge or corona discharge with a frequency offrom 50 Hz to 1 MHz. In particular variants of non-thermal plasmaspraying, it is preferred that work is done at a frequency of from 10kHz to 100 kHz. The temperature of the plasma here is preferably lessthan 3000 K, preferably less than 2500 K and still more preferably lessthan 2000 K. This minimizes the technical outlay and keeps the input ofenergy into the coating material to be applied as low as possible, whichin turn allows a gentle coating of the substrate. The order of magnitudeof the temperature of the plasma flame is thus preferably comparable tothat of flame spraying or of high-speed flame spraying. Non-thermalplasmas the core temperature of which is below 1173 K or even below 773K in the core region can also be generated by targeted choice of theparameters. The temperature in the core region is measured here, forexample, using an NiCr/Ni thermocouple and a spray diameter of 3 mm at adistance of 10 mm from the nozzle outlet in the core of the emergingplasma jet at ambient pressure. Such non-thermal plasmas are suitable inparticular for coatings of very temperature-sensitive substrates.

To produce coatings with sharp boundaries without the need to coverareas in a targeted manner, it has proved to be advantageous to design,in particular, the outlet opening for the plasma flame such that thetrack widths of the coatings produced lie between 0.2 mm and 10 mm. Thismakes a very precise, flexible, energy-efficient coating possible whilemaking the best possible use of the coating material used. For example,a distance of 1 mm is chosen as the distance from the spray lance to thesubstrate. This makes possible as great a flexibility as possible of thecoatings and, at the same time, guarantees high-quality coatings. Thedistance between spray lance and substrate expediently lies between 1 mmand 35 mm.

Various gases known to a person skilled in the art and mixtures thereofcan be used as ionizable gas in the non-thermal plasma method. Examplesof these are helium, argon, xenon, nitrogen, oxygen, hydrogen or air,preferably argon or air. A particularly preferred ionizable gas is air.

For example to reduce the noise load, it can also be preferred here thatthe speed of the plasma stream lies below 200 m/s. For example, a valueof between 0.01 m/s and 100 m/s, preferably between 0.2 m/s and 10 m/s,can be chosen as the flow rate. In particular embodiments, it ispreferred in particular for example that the volume flow of the carriergas lies between 10 and 25 l/min, more preferably between 15 and 19l/min.

According to a preferred embodiment, the particles of the powderedcoating material are preferably metallic particles or metal-containingparticles. It is preferred in particular that the metal content of themetallic particles or metal-containing particles is at least 95 wt.-%,preferably at least 99 wt.-%, still more preferably at least 99.9 wt.-%.In particular preferred embodiments, the metal is, or the metals are,selected from the group consisting of silver, gold, platinum, palladium,vanadium, chromium, manganese, cobalt, germanium, antimony, aluminum,zinc, tin, iron, copper, nickel, titanium, silicon, alloys and mixturesthereof. In particular ones of the above-named embodiments, it ispreferred in particular that the metal is, or the metals are, selectedfrom the group consisting of silver, gold, aluminum, zinc, tin, iron,copper, nickel, titanium, silicon, alloys and mixtures thereof,preferably from the group consisting of silver, gold, aluminum, zinc,tin, iron, nickel, titanium, silicon, alloys and mixtures thereof.

According to further preferred embodiments of the method according tothe invention, the metal or the metals of the particles of the powderedcoating material is or are selected from the group consisting of silver,aluminum, zinc, tin, copper, alloys and mixtures thereof. In particular,metallic particles or metal-containing particles in which the metal is,or the metals are, selected from the group consisting of silver,aluminum and tin have proved to be particularly suitable particles inspecific embodiments.

In further embodiments of the invention, the powdered coating materialconsists of inorganic particles which are preferably selected from thegroup consisting of carbonates, oxides, hydroxides, carbides, halides,nitrides and mixtures thereof. Mineral and/or metal-oxide particles areparticularly suitable.

In other embodiments, the inorganic particles are alternatively oradditionally selected from the group consisting of carbonaceousparticles or graphite particles.

A further possibility is the use of mixtures of the metallic particlesand the above-named inorganic particles, such as for example mineraland/or metal-oxide particles, and/or the particles which are selectedfrom the group consisting of carbonates, oxides, hydroxides, carbides,halides, nitrides and mixtures thereof.

Furthermore, the powdered coating material can comprise or consist ofglass particles. In particular embodiments, it is preferred inparticular that the powdered coating material comprises or consists ofcoated glass particles.

In addition, in particular embodiments, the powdered coating materialcomprises or consists of organic and/or inorganic salts.

In still other embodiments of the present invention, the powderedcoating material comprises or consists of plastic particles. Theabove-named plastic particles are formed for example from pure or mixedhomo-, co-, block or pre-polymers or mixtures thereof. Here, the plasticparticles can be pure crystals or be mixed crystals or have amorphousphases. The plastic particles can be obtained for example by mechanicalcomminution of plastics.

In particular embodiments of the method according to the invention, thepowdered coating material comprises or consists of mixtures of particlesof different materials. In particular preferred embodiments, thepowdered coating material consists in particular of at least two,preferably three, different particles of different materials.

The particles can be produced via different methods. For example, themetal particles can be obtained by nebulizing or atomizing moltenmetals. Glass particles can be produced by mechanical comminution ofglass or else from the melt. In the latter case, the glass melt canlikewise be atomized or nebulized. Alternatively, melted glass can alsobe comminuted on rotating elements, for example a drum.

Mineral particles, metal-oxide particles and inorganic particles whichare selected from the group which consists of oxides, hydroxides,carbonates, carbides, nitrides, halides and mixtures thereof can beobtained by comminuting the naturally occurring minerals, stones, etc.and then screening them by size.

The screening by size can be carried out for example by means ofcyclones, air separators, screens, etc.

In particular embodiments of the present invention, the particles of thepowdered coating material have been equipped with a coating in additionto the surface coverage according to the invention. This makes itpossible for example to provide a coated standard powder with anincreased oxidation stability which is adapted to specific devices oruses by a targeted, subsequent surface coverage. This is particularlyadvantageous for a surface coverage according to the invention which isapplied by means of methods that are simple in terms of processengineering. In particular embodiments, therefore, it is preferred inparticular that the above-named coating is applied before the surfacecoverage according to the invention, wherein the surface coverageaccording to the invention is preferably applied mechanically to theparticles, for example kneaded on.

In particular preferred embodiments of the present invention, theabove-named coating can comprise a metal or consist of a metal. Such acoating of a particle can be formed closed or particulate, whereincoatings with a closed structure are preferred. The layer thickness ofsuch a metallic coating preferably lies below 1 μm, more preferablybelow 0.8 μm and still more preferably below 0.5 μm. In particularembodiments, such coatings have a thickness of at least 0.05 μm, morepreferably of at least 0.1 μm. Metals that are particularly preferred inparticular embodiments for use in one of the above-named coatings,preferably as main constituents, are selected from the group consistingof copper, titanium, gold, silver, tin, zinc, iron, silicon, nickel andaluminum, preferably from the group consisting of gold, silver, tin andzinc, further preferably from the group consisting of silver, tin andzinc. The term main constituent within the meaning of the above-namedcoating denotes that the relevant metal or a mixture of the above-namedmetals represents at least 90 wt.-%, preferably 95 wt.-%, furtherpreferably 99 wt.-% of the metal content of the coating. It must beunderstood that, in the case of a partial oxidation, the oxygenproportion of the corresponding oxide layer is not taken into account.Such metallic coatings can be produced for example by means of gas-phasesynthesis or wet-chemical methods.

In further particular embodiments, the particles according to theinvention of the powdered coating material are additionally oralternatively coated with a metal oxide layer. Preferably, this metaloxide layer substantially consists of silicon oxide, aluminum oxide,boron oxide, zirconium oxide, cerium oxide, iron oxide, titanium oxide,chromium oxide, tin oxide, molybdenum oxide, oxide hydrates thereof,hydroxides thereof and mixtures thereof. In particular preferredembodiments, the metal oxide layer substantially consists of siliconoxide. The above-mentioned term, “substantially consists of”, within themeaning of the present invention means that at least 90%, preferably atleast 95%, more preferably at least 98%, still more preferably at least99% and most preferably at least 99.9% of the metal oxide layer consistsof the above-named metal oxides, in each case relative to the number ofparticles of the metal oxide layer, wherein any water contained is notfactored in. The composition of the metal oxide layer can be determinedby means of methods known to a person skilled in the art, such as forexample sputtering in combination with XPS or TOF-SIMS. In particularones of the above-named embodiments, it is preferred in particular thatthe metal oxide layer does not represent an oxidation product of a metalcore located underneath it. Such a metal oxide layer can be applied forexample using the sol-gel method.

In particular preferred embodiments, the substrate is selected from thegroup consisting of plastic substrates, inorganic substrates,cellulose-containing substrates and mixtures thereof.

The plastic substrates can be for example plastic films or shaped bodiesmade of plastics. The shaped bodies can have geometrically simple orcomplex shapes. The plastic shaped body can be for example a componentfrom the automotive industry or the construction industry.

The cellulose-containing substrates can be cardboard, paper, wood,wood-containing substrates, etc.

The inorganic substrates can be for example metallic substrates, such assheet metals or metallic shaped bodies or ceramic or mineral substratesor shaped bodies. The inorganic substrates can also be solar cells orsilicon wavers, to which for example electrically conductive coatings orcontacts are applied.

Substrates made of glass, such as for example glass panes, can also beused as inorganic substrates. The glass, in particular glass panes, canbe equipped for example with electrochromic coatings using the methodaccording to the invention.

The substrates coated by means of the method according to the inventionare suitable for very different uses.

In particular embodiments, the coatings have optical and/orelectromagnetic effects. Here, the coatings can bring about reflectionsor absorptions. Furthermore, the coatings can be electricallyconductive, semiconductive or non-conductive.

Electrically conductive layers can be applied for example in the form ofstrip conductors to components. This can be used for example to makecurrent-carrying possible within the framework of the on-board powersupply in an automobile component. Furthermore, such a strip conductorcan, however, also be formed for example as an antenna, as a shield, asan electrical contact, etc. This is particularly advantageous forexample for RFID applications (radio frequency identification).Furthermore, coatings according to the invention can be used for examplefor heating purposes or for the targeted heating of specific componentsor specific parts of larger components.

In further particular embodiments, the coatings produced act as slidinglayers, diffusion barriers for gases and liquids, wear and/or corrosionprotection layers. Furthermore, the coatings produced can influence thesurface tension of liquids or have adhesion-promoting properties.

The coatings produced according to the invention can furthermore be usedas sensor surfaces, for example as human-machine interface (HMI), forexample in the form of a touchscreen. The coatings can likewise be usedto shield from electromagnetic interferences (EMI) or to protect againstelectrostatic discharges (ESD). The coatings can also be used to bringabout electromagnetic compatibility (EMC).

Furthermore, through the use of the particles according to theinvention, layers can be applied which are applied for example toincrease the stability of corresponding components after repair. Anexample is constituted by repairs in the aviation sector, wherein forexample a loss of material as a result of processing steps must becompensated for, or a coating is to be applied for example forstabilization. This proves to be difficult for aluminum components forexample, and normally requires post-processing steps such as sintering.In contrast, by means of the methods according to the invention, firmlyadhering coatings can be applied under very gentle conditions, withoutpost-processing steps such as sintering even being required.

In still other embodiments, the coatings act as electrical contacts andallow an electrical connection between different materials.

A person skilled in the art is aware that the specifications indicatedabove with regard to the method according to the invention in respect ofthe powdered coating material and the particles contained therein alsoapply correspondingly to the use of the powdered coating material andthe particles contained therein, and vice versa.

FIGURES

FIGS. 1 and 2 show a copper layer applied to a steel sheet.

EXAMPLES

Materials and methods used.

The size distribution of the particles of the powdered coating materialsused was determined by means of a HELOS device (Sympatec, Germany). Forthe measurement, 3 g of the powdered coating material was introducedinto the measuring device and treated, before the measurement, withultrasound for 30 seconds. For the dispersion, a Rodos T4.1 dispersingunit was used, wherein the primary pressure was 4 bar. The evaluationwas carried out with the device's standard software.

The method according to the invention is now explained in more detailwith reference to the following examples, without being limited to theexamples.

Example 1 Powdered Coating Materials Covered with1,10-decanedicarboxylic acid

3 g of 1,10-decanedicarboxylic acid was used as coating additive anddissolved in 50 g ethyl acetate. This mixture was then introduced,together with 240 g aluminum particles (D₅₀=2 μm), into a kneader(Duplex kneader from IKA) and kneaded for 30 min at RT (20° C.). Atemperature of 40° C. and a vacuum of 250 mbar were then set. Drying wascarried out for 1 h and then the particles covered with the coatingadditive were removed from the kneader and then screened (71 μm).

Example 2 Powdered Coating Materials Covered with Monoethyl Fumarate

The application of the coating additive was carried out analogously toExample 1. 3 g monoethyl fumarate was used as coating additive.

Example 3 Powdered Coating Materials Covered with Adipic Acid MonoethylEster

The application of the coating additive was carried out analogously toExample 1. 3 g adipic acid monoethyl ester was used as coating additive.

Example 4 Powdered Coating Materials Covered with Methyl Triglycol

The application of the coating additive was carried out analogously toExample 1. 3 g methyl triglycol was used as coating additive.

Example 5 Powdered Coating Materials Covered with Adipic Acid MonoethylEster

The application of the coating additive was carried out analogously toExample 1. However, copper particles with a D₅₀ of 34 μm were used here.3 g adipic acid monoethyl ester was used as coating additive.

Example 6 Powdered Coating Materials Covered with Methyl Triglycol

The application of the coating additive was carried out analogously toExample 1. However, a copper particle with a D₅₀ of 34 μm was used here.3 g methyl triglycol was used as coating additive.

Example 7 Powdered Coating Materials Covered with Ethocel 7-1: CopperParticles

The application of the coating additive was carried out analogously toExample 1. Copper particles with a D₅₀ value of 34 μm were used here. 3g ethyl cellulose (Ethocel Standard 10, from Dow Wolff Cellulosics) wasused as coating additive.

7-2: Aluminum Particles

The application of the coating additive was carried out analogously toExample 1. 100 g aluminum particles with a D₅₀ value of 1.6 μm were usedhere. 3 g ethyl cellulose (Ethocel Standard 10, from Dow WolffCellulosics) was used as coating additive.

Example 8 Powdered Coating Materials Covered with Monoethyl Fumarate

The application of the coating additive was carried out analogously toExample 1. A copper particle with a D₅₀ value of 34 μm was used here. 3g DEGALAN PM 381 (copolymer from methyl methacrylate and isobutylmethacrylate, from Evonik) was used as coating additive.

Example 9 Powdered Coating Materials Covered with Polyacrylate

The copper paste or tin paste was dispersed in 600 g ethanol, with theresult that a 35 wt.-% dispersion formed. 100 ml of a solution of 0.5 gdimethyl 2,2′-azobis(2-methylpropionate) (trade name V 601; availablefrom WAKO Chemicals GmbH, Fuggerstraβe 12, 41468 Neuss), 1 gmethacryloxypropyltrimethoxysilane (MEMO) and 10 g trimethylolpropanetrimethacrylate (TMPTMA) in white spirit was then added to the reactionmixture over 1 h. Stirring followed for a further 15 h at 75° C., thereaction mixture was filtered off, isolated as paste and dried undernegative pressure.

Example Metal D50 9-1 Aluminum grit 1.6 μm  9-2 Copper grit 25 μm 9-3Copper flakes 35 μm 9-4 Copper grit  9 μm 9-5 Tin grit 28 μm

The decomposition temperature of the polymer here was approx. 260° C.,determined according to DIN EN ISO 11358. At this temperature, anincipient clear decrease in the weight of the powdered coating materialwas shown.

Example 10 Flame Spraying 10-1: Application of Examples 1 to 4

Using a flame spraying system from CASTOLIN, aluminum particles with aD₅₀ value of 2 μm without coating additive, as well as the aluminumparticles according to Examples 1 to 4, were applied to a sheet by meansof an oxy-acetylene flame. Furthermore, copper particles with a D₅₀value of 34 μm without coating additive, as well as the copper particlesaccording to Examples 5 to 8, were applied analogously. The obtainedsheets were examined by means of SEM.

The sheets coated according to the invention were much more homogeneousin relation to their optics as well as their haptics. SEM photographs ofthe surfaces demonstrate the formation of larger uniform areas of thecoating, while the surface of the comparison examples is characterizedby a large number of isolated particles. Furthermore, the cross-sectionshows that cavities contained in the coating of the sheet according tothe invention are significantly smaller.

10-2: Application of Examples 7-2 and 9-1

The aluminum particles according to Examples 7-2 and 9-1 were applied tosteel sheets by means of a flame spraying system from CASTOLIN in anoxy-acetylene flame. The obtained sheets were then analyzed by means ofSEM. A uniform coating was shown here, wherein small cavities and onlynegligible amounts of oxidation were observed. The coatingsmacroscopically showed a good adhesion to the steel sheets.

The application of aluminum particles according to Example 9-1 withoutcoating additive did not allow a coating according to the invention.Only small quantities of greatly isolated, very coarse particulateparticle agglomerates were applied to the surface here.

Example 11 Non-Thermal Plasma Spraying

The powdered coating material was applied by means of a Plasmatronsystem from Inocon, Attnang-Puchheim, Austria. Argon and nitrogen wereused as ionizable gases. Standard process parameters were used here.

Examples 9-2 to 9-5 were applied to alu sheets, steel sheets and wafers.Here, a very uniform application of the powder, a small overspray, agood adhesion of the layer to the surface and a color of the coatingwhich allows a small quantity of oxidation to be deduced were shown.This was also confirmed in subsequent SEM photographs. Examples ofphotographs of the coating with spherical copper grit according toExample 9-2 are found in FIGS. 1 and 2. For example the excellentbinding to the surface is recognizable from FIG. 1. FIG. 2 shows thesurprisingly uniform distribution of the individual particles inrelation to the size of the individual particles (D₅₀=25 μm).

Attempts to apply particles without coating additive by means ofnon-thermal plasma spraying did not result in any usable coatings. Inparticular, no continuous coating could be achieved with this.Agglomerates occurring on the surface showed no noticeable binding tothe substrate surface.

1. A process for producing a coating comprising: introducing aparticle-containing powdered coating material in a coating methodselected from the group consisting of cold gas spraying, flame spraying,high-speed flame spraying, thermal plasma spraying and non-thermalplasma spraying, wherein the particles on the surface are at leastpartially covered with at least one coating additive which has a boilingpoint or decomposition temperature of below 500° C.
 2. The processaccording to claim 1, wherein the weight proportion of the at least onecoating additive is at least 0.01 wt.-%, relative to the total weight ofthe coating material and the coating additive.
 3. The process accordingto claim 1, wherein the weight proportion of the at least one coatingadditive at most 80 wt.-%, relative to the total weight of the coatingmaterial and the coating additive.
 4. The process according to claim 1,wherein the particles comprise metal particles, and the metal isselected from the group which consists of silver, gold, platinum,palladium, vanadium, chromium, manganese, cobalt, germanium, antimony,aluminum, zinc, tin, iron, copper, nickel, titanium, silicon, alloys andmixtures thereof.
 5. The process according to claim 1, wherein thecarbon content of the powdered coating material is from 0.01 wt.-% to 15wt.-%, in each case relative to the total weight of the coating materialand the coating additive.
 6. The process according to claim 1, whereinthe compounds used as coating additive has at least 6 carbon atoms. 7.The process according to claim 1, wherein the coating method is selectedfrom the group consisting of flame spraying and non-thermal plasmaspraying.
 8. The process according to claim 1, wherein the at least onecoating additive is selected from the group consisting of polymers,monomers, silanes, waxes, oxidized waxes, carboxylic acids, phosphonicacids, derivatives of the above-named and mixtures thereof.
 9. Theprocess according to claim 1, wherein the at least one coating additivecomprises no is free of stearic acid and/or oleic acid.
 10. The processaccording to claim 1, wherein the coating additive is appliedmechanically to the particles.
 11. The process according to claim 1,wherein the powdered coating material has a particle-size distributionwith a D₅₀ value from a range of from 1.5 to 53 μm.
 12. A method forcoating a substrate selected from the group consisting of cold gasspraying, flame spraying, high-speed flame spraying, thermal plasmaspraying and non-thermal plasma spraying, the method comprising (a)introducing a particle-containing powdered coating material into amedium directed onto a substrate to be coated by cold gas spraying,flame spraying, high-speed flame spraying, thermal plasma spraying ornon-thermal plasma spraying, wherein the particles are covered with atleast one coating additive which has a boiling point or decompositiontemperature of below 500° C.
 13. The method according to claim 12,wherein the coating method is selected from the group consisting offlame spraying and non-thermal plasma spraying.
 14. The method accordingto claim 12, wherein the powdered coating material is conveyed as anaerosol.
 15. The method according to claim 12, wherein the mediumdirected onto the substrate is air or has been produced from air. 16.The process and according to claim 1, wherein the coating method isnon-thermal plasma spraying.
 17. The method according to claim 12,wherein the coating method is non-thermal plasma spraying.
 18. Theprocess according to claim 1, wherein the at least one coating additivecomprises polymer(s), monomer(s), silane(s), wax(es), oxidized wax(es),carboxylic acid(s), phosphonic acid(s), derivatives of carboxylicacid(s), derivatives of phosphonic acid(s), or mixtures thereof.
 19. Theprocess according to claim 1, wherein the at least one coating additivecomprises acrylate and/or methacrylate.
 20. The process according toclaim 1, wherein the at least one coating additive comprisesorganofunctional silane.
 21. The process according to claim 1, whereinthe weight proportion of carbon atoms in the powdered coating materialranges from 0.01 weight percent to 15 weight percent.